Tray Table Positioning; Tray Table Slots; Light Sensors - Sony CDP-CX235 Training Manual

Tray Table Positioning

In order for the tray table to be positioned, two rows of slots are molded
into the bottom of the rotating tray table forming rings. These slots mate
with light sensors stationed on the bottom of the CD Changer. The sen-
sors feed back information to Syscon so it can determine the exact tray
table position.

Tray Table Slots

At the bottom of the tray table, outer ring (#2) contains 200 equally spaced
slots that look like teeth. Each slot consists of an empty area (gap) in the
plastic ring that passes light and an equal width tooth that blocks the light.
One ring #2 slot corresponds to one disc slot.
Inner ring (#1) contains different spaced gaps. Ring 1's smallest gap is
equal in width to one slot and one tooth pair in ring 2. Ring 1's largest gap
is the width of ten of ring 2's slots and teeth (10 disc slots). Generally, the
width of a gap is one for each group of 10 disc slots.
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Light Sensors

Each light interrupt sensor forms a U channel. At one side of the sensor
there is an infrared LED that shines light through the channel. At the
other end is a phototransistor that monitors this light. When light passes
through the channel (light is received by the phototransistor), the electri-
cal output is HIGH. When the channel is blocked, there is no electrical
output.
All three sensors are used to locate the tray position as the tray rotates.
Sensor IC801 monitors the gaps in ring #1. Sensors IC802 and IC803
are both used to monitor the gaps in ring #2. IC802 and IC803 sensors
are positioned off center to determine the center of the slot. This off
center information is necessary so the tray can stop the CD exactly in
front of the CD Mechanism each time.
IC801's sensor records Ring #1's gap width. These gaps increase as the
number of disc slots increase. Therefore with a minimum rotation of the
tray table, the home position can be calculated using the data from IC801
and one of the slot sensors like IC802.